The present invention involves a new and improved method of distributing rock dust, particularly for use in underground coal mines.
The risk of explosion associated with the accumulation of coal dust is well-known in the underground coal mining industry. This risk is minimized through the use of rock dust which is distributed near the working face so that a thick layer of rock dust is deposited in the mine entry on the newly exposed mine floor, ribs and roof. In addition, secondary rock dusting operations are required to distribute rock dust in previously excavated mine entries for the purposes of settling out any coal dust which may be entrained in the ventilation air stream of the mine and to maintain the desired layer of rock dust on the mine floor, ribs and roof throughout the mine.
In practice, rock dusting operations are generally accomplished with the use of rock dusting machines. These machines, however, generally require continuous attention by one or more operators, distribute large quantities of rock dust undiscriminatingly and therefore inefficiently, or require the use of other underground mining equipment thereby interfering with production schedules. In addition, these machines generally fall into two categories. First, there are those machines which use complex mechanisms with numerous moving parts to transport the rock dust through the machine and to then distribute the rock dust into the mine entry thereby causing wear on the parts which come in contact with the rock dust. Such machines are described in U.S. Pat. No. 3,871,588 issued Mar. 18, 1975, U.S. Pat. No. 4,510,883 issued Apr. 16, 1985, U.S. Pat. No. 4,673,131 issued Jun. 16, 1987 and U.S. Pat. No. 4,805,702 issued Feb. 21, 1989. Second, there are those machines which rely upon a combination of gravity and pressure differentials, known in the art as venturi effect, to move and distribute the rock dust. The machines which use gravity and pressure differentials generally use small tubes or orifices through which the rock dust must pass and are therefore susceptible to the bridging of the rock dust or otherwise clogging, especially if the rock dust has become wet or otherwise absorbed any moisture, thereby preventing the rock dust from being distributed as required. These types of machines are described in U.S. Pat. No. 3,809,439 issued May 7, 1974, U.S. Pat. No. 4,394,975 issued Jul. 26, 1983 and U.S. Pat. No. 4,538,941 issued Sep. 3, 1985.
Thus, there is a need for a simple rock dusting apparatus which requires little operator attention, which does not interfere with production schedules and which can provide the continuous and controllable distribution of rock dust as needed.